There are many important applications in the electronics art wherein it is highly desirable, or necessary, controlledly to connect one or more multiple contact source ports to one or more signal utilization ports in any desired combination. In some cases it may be desirable to control the connection of a single source port to any of a plurality of signal utilization ports or to connect any of a plurality of source ports to one signal utilization port, but in general there may be a plurality of both source ports and signal utilization ports to be controlledly interconnected.
The problem with providing such controlled switching becomes increasingly more difficult as the number of source ports and/or signal utilization ports is increased, and the problem becomes particularly severe when the number of signals in each port is large. For example, the standard RS-232 port provides 24 signals (plus ground), one of which typically carries a serial data signal and the others of which typically carry auxiliary information, for example timing and control signals for effecting the desired communication of the serial data signal. While in some cases all 24 of the signals need not be utilized, even when less than all of the signals are used the complications of the switching operation can become unduly burdensome. Where the switching system is to be of most general utility the problem is most severe, in that it should be able to provide controlled switching of all 24 of the port signals since, in a given situation, any one of the signals or all of them may be utilized. If, as is not unusual, there are 128 source ports and 128 utilization or destination ports, it would be necessary to provide a matrix having 393,216 crosspoint switching elements to effect the desired switching by conventional means.
Accordingly, other methods of accomplishing such switching have been proposed and employed, including the time-division multiplexed-bus switch in which the source and the destination ports are all connected to a common bus containing a line for each corresponding contact of the ports, so that by turning on any selected source port and any selected destination port at the same instant, the desired communication can be accomplished momentarily for any selected pair of such devices. Since communication is desired between all source devices and destination devices, each of the destination devices is switched on momentarily and repetitively when each of the source device is switched on, in time-multiplex fashion. In order for this to be effective, especially with signals embodying high data rates, the switching must be accomplished at extremely high rates. For example, if a 9600 baud signal is to be transferred with no more than 12.5% distortion, then it must be sampled at least 76,800 times per second. If 256 such sets of signals are to be switched over the same bus, then the aggregate sampling rate of the bus must be at least 19,660,800 samples per second. More signals, higher speeds, and lower distortion all require even higher sampling rates on the high speed bus so that the overall performance of this type of switching is limited by the bandwidth that is available on the high speed bus.
The present invention provides a signal switching system which is not subject to the bandwidth limitations of the above-described time-multiplexed common bus system, and which does not require the large number of switching elements required by the standard matrix switching also described above.
It is therefore an object of the present invention to provide a new and useful signal switching system.
Another object is to provide such system which does not require the large number of switching elements or the high bandwidth required of previous systems for accomplishing comparable switching.